The present invention relates to a mask used for producing a semiconductor device, a method of producing the same, and a method of producing a semiconductor device.
Along with miniaturization of semiconductor devices, it has become more difficult to form micropatterns by lithography utilizing ultraviolet light. Therefore, lithography technologies using X-rays, electron beams, ion beams, etc. have been proposed, researched, and developed.
As previously proposed electron beam transfer type lithography techniques, PREVAIL (projection exposure with variable axis immersion lenses) developed jointly by IBM and Nikon, SCALPEL (scattering with angular limitation in projection electron-beam lithography) developed by Lucent Technologies etc., and LEEPL (low energy electron-beam proximity projection lithography) developed jointly by LEEPL Corporation, Tokyo Seimitsu Co., Ltd., and Sony can be mentioned.
For PREVAIL and SCALPEL, a high energy electron beam of an acceleration voltage at about 100 kV is used. In the case of PREVAIL and SCALPEL, an electron beam passing through part of a mask is focused on a resist by a reduction projection system of a scale factor of usually 4 to transfer the patterns.
For LEEPL, a low energy electron beam of an acceleration voltage at about 2 kV is used (T. Utsumi, Low-Energy E-Beam Proximity Lithography (LEEPL) Is the Simplest the Best? Jpn. J. Appl. Phys. Vol. 38 (1999) pp. 7046-7051). In the case of LEEPL, the electron beam passes through holes provided in a mask to transfer patterns on a resist at the same scale.
LEEPL has an advantage in simplifying the configuration of the electron lens barrel compared with PREVAIL and SCALPEL. Also, generally, the higher the acceleration voltage of the electrons, the less the scattering of the electrons in the resist and the less probability of reaction of the electrons and the resist. Therefore, in lithography utilizing a high energy electron beam, a more sensitive resist is required. As opposed to this, in LEEPL, since the energy of the electron beam is low, the resist can be used at a high sensitivity and a high productivity can be realized.
FIG. 1 is a schematic view of LEEPL exposure. As shown in FIG. 1, a stencil mask 101 used for LEEPL has a thin film (membrane) 102. Holes 103 corresponding to the patterns are formed in the membrane 102. The membrane 102 is a part of a membrane formation layer 102a. The membrane formation layer 102a around the membrane 102 is formed with a support frame (frame) 104 for reinforcing the mechanical strength of the stencil mask 101.
The stencil mask 101 is arranged in proximity to the surface of a wafer 105. The wafer 105 is coated with a resist 106. When scanning the stencil mask 101 by an electron beam 107, the electron beam 107 passes through only the portions of the holes 103 so the patterns are transferred on the resist 106. Since LEEPL is same scale exposure, it was necessary in conventional LEEPL to make the size of the membrane 102 several mm to several 10 mm square or equal to the size of a LSI chip on which the patterns are transferred.
FIG. 2 is an enlarged perspective view of part of the membrane 102 of FIG. 1. As shown in FIG. 2, the membrane 102 is formed with holes 103 corresponding to the micropatterns. For etching the membrane 102 to form the holes 103 with a high precision, generally a ratio of the membrane thickness to the diameter of the holes 103 (aspect ratio) must be 10 or less, preferably 5 or less. Therefore, when forming the holes 103 for the patterns having a line width of for example 50 nm in a stencil mask for production of a device of the 0.10 xcexcm or later generation, it is necessary to make the membrane thickness 500 nm or less.
The thinner the membrane thickness, the more precisely the holes 103 can be formed. However, a membrane 102 formed thinly easily flexes. If the membrane flexes, the transferred patterns may distor or the transferred patterns may become offset in position. Therefore, the membrane 102 is formed so that tensile stress occurs inside. The larger the area of the membrane 102, the greater the internal stress required for flattening the membrane 102.
FIG. 3 shows the change of deflection and internal stress of a membrane depending on the membrane area. Here, the membrane is made a rectangular shape with four fixed sides. The length of one side is indicated on an abscissa of FIG. 3. The deflection shows the deflection at the center of the membrane due to gravity, while the stress shows the stress occurring at the center of the membrane. FIG. 3 shows an example of calculation for a silicon nitride film having a thickness of 200 nm assuming a Young""s modulus of 300 GPa.
Flattening the membrane requires an internal stress able to cancel out the stress at the center. In the example of FIG. 3, when the membrane size becomes larger than 10 mm square, the stress at the center will exceed 10 MPa. Therefore, an internal tensile stress of 10 MPa or more is required at the membrane.
Although it is possible to increase the internal stress to fabricate the membrane, if forming holes in a membrane in the state of a large internal stress, the internal stress is released at the hole parts. Therefore, as shown in for example FIG. 2, when forming a plurality of holes of different shapes from each other unevenly in the membrane or forming holes having large diameters, offset or distortion of the patterns easily occurs around the holes.
Separate from the above problems, in the case of a stencil mask, there is the restriction that formation of specific patterns requires use of a complementary mask. A membrane mask comprised, without holes, of a substrate formed with a light-blocking film (or bodies for scattering a charged particle beam) may be formed topologically with donut-shaped interconnection patterns without problem. As opposed to this, in the case of a stencil mask, since all of the parts except the holes must be connected, when forming donut-shaped interconnection patterns, it is necessary to divide the patterns among a plurality of masks and to perform multiple exposure using these masks.
Alternatively, when forming holes corresponding to long line-shaped patterns, anisotropic distortion occurs in the pattern shapes due to the influence of the internal stress so the line width will not become even or stress will concentrate at corners of the patterns and the membrane will easily break. Therefore, long line-shaped patterns are also sometimes divided into a plurality of rectangles and continuous patterns are transferred by multiple exposure.
In the above way, when using a stencil mask for electron beam transfer type lithography, multiple exposure using a plurality of masks is assumed and the patterns have to be aligned with a high accuracy.
Further, in recent semiconductor devices, the number of interconnection layers forming the multilayer interconnections has been increasing. Securing alignment accuracy of the patterns between layers has been becoming increasingly difficult.
The present invention was made in consideration of the above problems and has as its object to provide a mask able to prevent a drop in pattern alignment accuracy due to the internal stress of the membrane and able to align patterns including complementary patterns at a high accuracy, a method of producing the same, and a method of producing a semiconductor device.
To achieve the above object, the mask of the present invention is characterized by comprising a support frame; a thin film formed thinner than the support frame and surrounded by the support frame; a first section comprised of one of four sections consisting of regions obtained by dividing the thin film into four by a first straight line passing through a first point consisting of one point on the thin film and extending in a first direction and a second straight line orthogonal to the first straight line at the first point and extending in a second direction; a second section adjacent to the first section in the first direction; a third section adjacent to the second section in the second direction; a fourth section adjacent to the third section in the first direction and adjacent to the first section in the second direction; a first group of struts, in each of the first to fourth sections, comprised of a plurality of struts formed from the same material as the support frame, extending in the first direction, and formed in parallel with each other at equal intervals so as to connect with the support frame on the thin film; a second group of struts, in each of the first to fourth sections, comprised of a plurality of struts formed from the same material as the support frame, extending in the second direction, and formed in parallel with each other at equal intervals so as to connect with the support frame on the thin film and intersect the first group of struts; skirts provided in parallel to the struts at the thin film at the two side parts of the struts; strut zones comprised of the struts and the skirts at the two sides where the interval between adjacent strut zones becomes a whole multiple of at least 3 of the width of the strut zones, a first strut zone including one of the first group of struts formed in the first section and contacting the first straight line, the first strut zone being connected to the second group of struts of the fourth section at different locations from the second group of struts of the first section in the first direction, a second strut zone including one of the second group of struts formed in the first section and contacting the second straight line, the second strut zone being connected to the first group of struts of the second section at different locations from the first group of struts of the first section in the second direction, a third strut zone including one of the first group of struts formed in the third section and contacting the first straight line, the third strut zone being connected to the second group of struts of the second section at different locations from the second group of struts of the third section in the first direction, a fourth strut zone including one of the second group of struts formed in the third section and contacting the second straight line, the fourth strut zone being connected to the first group of struts of the fourth section at different locations from the first group of struts of the third section in the second direction; holes provided in the part of the thin film surrounded by the strut zones and passed through by a charged particle beam, the holes being formed by complementary divided patterns comprised of different parts of the same patterns in the first to fourth sections; and four superpositioned regions of the same shapes and sizes selected from the first to fourth sections, the superpositioned regions including the first and second straight lines, wherein any point on the superpositioned regions is included in the thin film other than the strut zones in at least two sections of the first to four sections.
The holes may be formed at least at parts of the skirts. Preferably, a plurality of alignment marks are provided at parts of the surfaces of the struts where the charged particle beam enters. The thin film may be an electroconductive layer. Alternatively, it is possible to provide an electroconductive layer formed on the thin film other than the hole parts.
To achieve the above object, the method of producing a semiconductor device of the present invention includes the step of irradiating a charged particle beam via a mask formed with predetermined mask patterns to transfer the mask patterns on the photosensitive surface and comprises using a mask of the present invention as the mask for multiple exposure of the complementary divided patterns formed in the first to fourth sections.
To achieve the above object, the mask of the present invention includes at least three masks, each mask comprising a support frame; a thin film formed thinner than the support frame and surrounded by the support frame, the thin film having the same shape and size among all of the masks; a plurality of blocks obtained by dividing the thin film into regions; a group of selected blocks composed of selected blocks selected from the plurality of blocks, the selected blocks being connected to at least two other selected blocks or connected to at least one other selected block and the support frame; holes formed in the thin film of non-selected blocks and passed through by a charged particle beam, in each mark, the holes formed in complementary divided patterns forming different parts of the same pattern; and struts formed on the thin film of the group of selected blocks, the struts connected to the support frame; all of the blocks becoming non-selected blocks in at least two of the masks.
The struts may be formed on a surface of the thin film at a side where the charged particle beam enters or the surface of the opposite side. Preferably, provision is made of a plurality of alignment marks at parts of the struts. The thin film may also be an electroconductive layer. Further, it is also possible to form an electroconductive layer on the thin film other than the hole parts. Preferably, the blocks are arranged in a lattice.
The method of producing a mask of the present invention is characterized by comprising the steps of forming a thin film on one surface of a substrate; forming struts on the thin film at predetermined intervals; removing a center of the thin film from the other surface of the substrate to expose the thin film and form a support frame comprised of the substrate; and forming holes through which a charged particle beam passes in part of the thin film surrounded by the struts.
Alternatively, it comprises the steps of forming a sacrifice film on one surface of a substrate; forming struts on the sacrifice film at predetermined intervals; removing a center part of the substrate from the other surface of the substrate to expose the sacrifice film and form a support frame comprised of the substrate; forming a thin film on a surface of the sacrifice film at the opposite side of the struts; forming holes through which a charged particle beam passes at parts of the thin film surrounded by the struts; and removing the parts of the sacrifice film not contacting the support frame.
The method of producing a semiconductor device of the present invention is characterized by including the step of irradiating a charged particle beam on a photosensitive surface via a mask on which complementary divided patterns forming parts of predetermined patterns are formed to transfer the complementary divided patterns on the photosensitive surface and the step of multiply exposing the photosensitive surface by the charged particle beam through masks on which other complementary divided patterns of the patterns are formed to transfer the patterns complementarily, characterized by using a complementary mask of the present invention comprised of at least three masks for the multiple exposure.
Due to this, it is possible to lower a tensile internal stress of the thin film as required for preventing deflection of the thin film. Therefore, displacement or distortion of holes due to release of the internal stress when forming the holes in the thin film is lowered. Further, mechanical strength of the thin film is reinforced. Further, it becomes possible to align precisely the entire membrane by providing alignment marks on the struts.